This invention relates to rotary drill bits and methods of fabrication, and more particularly to drill bits having hard abrasion and erosion resistant elements, such as internal fluid passages, within and on the bit.
Typically, earth boring drill bits include an integral bit body which may be of steel or may be fabricated of a hard matrix material such as tungsten carbide. A plurality of diamond or other "superhard" material cutting elements are mounted along the exterior face of the bit body. Each diamond cutting element typically has a backing portion which is mounted in a recess in the exterior face of the bit body. Depending upon the design of the bit body and the type of diamonds used (i.e., either natural or synthetic), the cutters are either positioned in a mold prior to formation of the bit body or are secured to the bit body after fabrication.
The cutting elements are positioned along the leading edges of the bit body so that as the bit body is rotated in its intended direction of use, the cutting elements engage and drill the earth formation. In use, tremendous forces are exerted on the cutting elements, particularly in the forward to rear tangential direction as the bit rotates, and in the axial direction of the bit. Additional, the bit body and cutting elements are subjected to substantial abrasive and erosive forces.
Typically, the rotary bit also includes a fluid flow passage or internal watercourse through the interior of the bit which splits into a plurality of passages or courses which are directed to the exterior surface of the bit. These passages, and the exit ports from which fluid is ejected, are positioned about the exterior surface of the bit and high velocity drilling fluid is directed against or across the cutting elements to cool and clean them and to remove adhering cuttings therefrom. The fluid also aids in washing the cuttings from the earth formation upwardly to and through so-called junk slots in the bit to the surface. Again, the high velocity flow of drilling fluid exerts erosive forces on the internal fluid passages, and, in combination with the cuttings, exerts tremendous erosive forces on the exterior surfaces of the bit. The bit also experiences abrasion from contact with the formation being drilled.
Steel body bits have been used to drill certain earth formations because of their toughness and ductility properties. These properties render them resistant to cracking and failure due to the impact forces generated during drilling. However, steel is subject during drilling operations to rapid erosion from high velocity drilling fluids, and to abrasion from the formation. The internal watercourses formed within the steel bit are also subject to the erosive forces of the drilling fluid.
Composite bits formed of a hard metal or mixture of metals including tungsten carbide have been used because they are more resistant to the abrasive and erosive forces encountered by the bit. Such rotary bits are generally formed by packing a graphite mold with a metal powder such as tungsten carbide, steel, or mixture of metals and then infiltrating the powder with a molten copper alloy binder. A steel blank is positioned in the mold and becomes secured to the matrix as the bit cools after furnacing. Also present in the mold may be a mandrel or a plurality of rigid sand cast elements which, when removed after furnacing, leave behind the internal fluid passages or watercourses through the bit. After molding and furnacing of the bit, the end of the steel blank can be welded or otherwise secured to an upper threaded body portion of the bit.
It would be desirable in the manufacture of rotary bits for drilling earth formations to be able to place erosion resistant elements on the surface of the bit as well as rendering the internal fluid passages in the bit more resistant to erosion. Accordingly, there is still a need in the art for rotary drill bits having erosion resistant elements both on the exterior surfaces of the bit as well as the interior of the bit.